Microbiologists have found that bugs deliberately taken into space on board the space shuttle Atlantis became three times more deadly than those cultivated on Earth.

The US scientists say the results are relevant for future space travel, particularly since missions are now being planned further afield and for much longer periods.

And they say their work could also have applications in the treatment of infectious diseases on Earth.

When Atlantis blasted off on a 12-day mission in September last year, it was carrying six astronauts and some salmonella. The bacteria was part of an experiment led by researchers from Arizona State University.

During the 12-day mission, one of the astronauts activated the growth of the bacteria. When the mission returned, the bugs were compared with a control batch cultured on Earth.

The space bugs were found to be three times as deadly to mice as the control bugs.

Cheryl Nickerson is an associate professor at the Centre for Infectious Diseases and Vaccinology at Arizona State University, and lead author of the study.

"We know that reports suggest that there are aspects of the astronauts' immune systems that don't function quite as well in flight as they do on the ground, and so that suggested increased risk for infectious disease events," she said.

"In particular, when we start looking at these future missions ... as we continue to push the frontiers and explore our universe, we're going to be extending both our duration, in terms of our length of time, that we send humans into space, and also they're going to be much further out in space and much further away from Earth than they have been.

"As we start to make those kinds of changes in space flight, there comes with that an increased risk of infectious disease."

Clinical use

Prof Nickerson says that deepening understanding of how the bacteria react in certain situations could also have applications in the treatment of infectious diseases on Earth.

"Using this new insight that we're gaining from culturing these bacteria - under ways that they normally encounter in the body, but we haven't paid a lot of attention to before - opens up the possibility that we can identify new targets that have a real potential to be translated to a clinical application, perhaps as a new drug or therapeutic or vaccine to treat the infections, whether it's for astronauts or for space tourists, or for us here on Earth," she said.

The astronaut who carried out the experiment on board Atlantis collapsed during a welcome home ceremony from the mission.

NASA experts attributed that to her adjusting to gravity.

And Assoc Prof Nickerson says the incident was totally unrelated to her work with the bacteria.

"At no time were the crew at any risk - this experiment was properly contained in triple containment levels for their safety," she said.

"Nor was anyone on the ground, or nor is anyone on the ground in any risk for these bacteria.

"Everyone actually has potential to benefit because of the novelty in the ways that this bug is now showing us that it's causing disease."